1. Field of the Invention
This invention relates generally to a corona ignition system, and a method of controlling corona discharge and arc formation provided by the corona ignition system.
2. Related Art
Corona discharge ignition systems provide an alternating voltage and current, reversing high and low potential electrodes in rapid succession. These systems include a corona igniter with an electrode charged to a high radio frequency voltage potential and creating a strong radio frequency electric field in a combustion chamber. The electric field causes a portion of a mixture of fuel and air in the combustion chamber to ionize and begin dielectric breakdown, facilitating combustion of the fuel-air mixture. During typical operation of the corona ignition system, the electric field is ideally controlled so that the fuel-air mixture maintains dielectric properties and corona discharge occurs, also referred to as a non-thermal plasma. The ionized portion of the fuel-air mixture forms a flame front which then becomes self-sustaining and combusts the remaining portion of the fuel-air mixture. The corona discharge has a low current and can provide a robust ignition without requiring a high amount of energy and without causing significant wear to physical components of the ignition system.
In a corona ignition system, good ignition characteristics are due to the corona discharge spreading over a large volume in a large number of filaments or streamers. If too much energy is applied to the corona igniter, it is possible for the corona discharge to extend from the high voltage source far enough to reach a grounded engine component. When this happens, a conductive path, referred to as an arc, is formed to the grounded component. The arc formation comprises a relatively high current flow and thus concentrates the ignition energy into a very limited volume, reducing ignition efficiency. It is typically desirable to avoid this situation. Conversely, it is difficult to be certain that a corona igniter is fed with enough energy to produce a large enough corona, as there is no direct method of obtaining the volume of the corona discharge.